Climate change is often described as the defining challenge of our time. One aspect of this challenge has, historically, been quantifying its impact on particular weather events.

Now, with the help of scientific developments, we are rapidly improving our understanding of how human activity influences the weather. This area of science is important for its role in the burgeoning field of climate litigation.

“Probabilistic event attribution science” may sound complex but the aim is straightforward: to determine the extent to which human-caused climate change has altered the probability or intensity of specific weather events.

While scientists use a range of methods to do this, the main approach is to compare real world scenarios with a simulated alternative that excludes man-made greenhouse gas emissions.

Take, for example, the Chinese city of Wuhan. In July 2016, torrential rain resulted in catastrophic flooding, which killed 237 people and left 93 missing. The flooding caused over US$22 billion in damage, making it one of the costliest weather-related natural disasters in Chinese history.

Chinese researchers wanted to understand how climate change affected the probability of this event happening. They found that extreme precipitation of that intensity was likely to occur once every 28 years, according to the climate of 2016. By contrast, in 1961, it would have been likely to occur once every 272 years. In other words, these events have become almost ten times more likely over 55 years.

Their findings suggested that around 60% of the risk of such an event occurring can be attributed to human-caused climate change. Climate change may, therefore, have substantially increased the probability of extreme rainfall such as that experienced in Wuhan.

Attribution science enables us to better understand what is happening today and produces clear evidence, and warnings, of future weather risks. This is important from a legal perspective, as foreseeability is fundamental to establishing a duty of care in many legal systems. Against this backdrop, the legal landscape is beginning to shift. This is partly due to scientific advances, but also due to the increasing losses of extreme weather events.

Litigation will fall into three main categories: i) failure to mitigate climate change, ii) failure to adapt to climate change, and iii) failure to comply with legislation or regulation around disclosing and reporting on climate change.

Failure to tackle the root causes

Failure to mitigate climate change includes claims for losses resulting from a public or private entity’s contribution to climate change, often through greenhouse gas emissions.

For example, Dutch citizens were recently successful in bringing a case against their government. The Hague Court of Appeal held that the government was acting in contravention of Articles 2 (right to life) and 8 (right to respect for private and family life) of the European Convention of Human Rights by failing to reduce greenhouse gas emissions by at least 25% by the end of 2020.

In another a case, a Peruvian farmer is bringing a claim against Germany’s largest electricity producer, RWE. He is seeking a contribution towards the cost of establishing flood protections to defend his hometown of Huarez against melting mountain glaciers caused by global warming. The case has not yet been tried but has been permitted to proceed to the evidential phase, where the court will consider evidence on RWE’s contributions to climate change, and the impact on mountain glaciers.

Event attribution science may be key to providing evidence of the extent of loss and damage that is attributable to climate change, rather than normal fluctuation in weather patterns. This has, historically, been challenging to establish.

Failure to adapt

Not adapting to climate change includes cases where it is alleged that an entity or individual has failed to take climate change risks into account in their decision-making. This goes beyond the physical risks of climate change and can encompass economic, reputational and legal risks.

For instance, the Boston-based Conservation Law Foundation filed a suit against ExxonMobil in 2016 with regard to its Everett Terminal in Massachusetts. The Foundation alleges that ExxonMobil was aware that a significant rise in sea level would put the terminal at risk but took no action to protect the public or the environment.

This type of claim is particularly relevant to governments, especially agencies that own and manage public infrastructure and assets. Many areas, such as infrastructure, will need to be upgraded to improve resilience to the physical consequences of climate change. By failing to monitor climate change science and integrate it into their decision-making processes, governments may be exposed to litigation.

In 2014, an insurance company sued local government municipalities in Chicago for failing to improve sewer and storm water drainage systems, despite knowing that climate change was making heavy rain more likely. Although the case was withdrawn, it remains an interesting example of the liability risks facing local governments.

This liability risk applies to private professionals and companies. For instance, engineers could see professional indemnity claims for failing to account for climate risks in projects.

Likewise, company directors and officers owe certain duties of care, which could be breached by a failure to take climate change risks into account, for example by not taking reasonable precautions to ensure their supply chains are resilient to climate impacts. In turn, this could lead to derivative actions by shareholders who have suffered loss as a result.

In all such cases, attribution science is set to play a key role in establishing whether extreme weather events, made more likely or intense as a result of climate change, are foreseeable. In turn, this may be used as a “standard of reasonableness” to gauge the actions of a wide range of individuals, companies and government bodies.

Failure to disclose information

Many companies are already required to disclose and report on risks in a way that is not misleading. Material risks posed by climate change are likely to be caught by existing regulations. Accordingly, a failure to adequately disclose the risks from climate change poses a legal threat for companies.

For instance, ClientEarth reported three insurance companies to the UK financial regulator in 2018 for failing to disclose climate change as a principal risk affecting the business in their annual reports. In all cases ClientEarth alleged that this failure constituted a breach of the disclosure guidance and transparency rules which apply to listed companies in the UK.

In a similar vein, New York’s attorney general recently sued ExxonMobil for misleading shareholders on the manner in which the company accounts for the effects of climate change. It is alleged that the company is more exposed to climate risk regulation than investors were led to believe.

For companies to adequately disclose the risks posed by climate change, they need to understand how climate change may impact their business. Attribution science enables companies to better understand and anticipate extreme weather events. Companies that fail to take advantage of this knowledge risk breaching the law.

As we improve our understanding of the degree to which climate change is expected to impact the weather, legal expectations as to how those impacts should be monitored and managed will inevitably increase.

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